alvindavis99

CIP School in the Phils.

Geometry: Perimeter Formulas

on August 23, 2012

 

A image of the perimeter of a rectangle.

A image of the perimeter of a rectangle. (Photo credit: Wikipedia)

(pi = pi = 3.141592…)

Perimeter Formulas
The perimeter of any polygon is the sum of the lengths of all the sides.

Note: “ab” means “a” multiplied by “b”. “a2” means “a squared”, which is the same as “a” times “a”.

Be careful!! Units count. Use the same units for all measurements. Examples

 

square = 4a

rectangle = 2a + 2b

 triangle = a + b + c   

circle = 2pi

circle = pid (where d is the diameter)

The perimeter of a circle is more commonly known as the circumference.

Units

Be sure to only add similar units. For example, you cannot add inches to feet.

For example, if you need to find the perimeter of a rectangle with sides of 9 inches and 1 foot, you must first change to the same units.

perimeter = 2 ( a + b)

INCORRECT
perimeter = 2(9 + 1) = 2*10 = 20

 

CORRECT
perimeter = 2( 9 inches + 1 foot)
= 2( 3/4 foot + 1 foot )
= 2(1 3/4 feet)
= 3 1/2 feet

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